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Lars B Clemmensen - One of the best experts on this subject based on the ideXlab platform.
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sea level proxies in holocene raised Beach Ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Mette Bendixen, Ronny Weβling, Lars B Clemmensen, Aart Kroon, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach Ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach Ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach Ridge systems represent long time intervals and only relatively small spatial extents.
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storm flood impacts along the shores of micro tidal inland seas a morphological and sedimentological study of the vesterlyng Beach the belt sea denmark
Geomorphology, 2016Co-Authors: Lars B Clemmensen, Aslaug C Glad, Aart KroonAbstract:Abstract The morphological and sedimentological impacts of an extreme storm event (‘Bodil’ in December 2013) were investigated at a mixed sand and gravel Beach (Vesterlyng) in a micro-tidal environment along the Belt Sea, Denmark. The storm response was characteristic for mixed sand and gravel Beaches: gravelly storm berms with sandy to gravelly washover fans were formed at the upper Beach where swash processes dominated during extreme water levels in combination with overtopping and overwash. In addition, storm scarps and gravel flats were formed. The elevation of the storm berm crest was identical to a summation of the still-water level (1.60 m) in the Belt Sea during the storm flood and the wave run-up (0.75 m) at the shore. The crest of 2.35 m is therefore a precise measure of the storm flood level. This storm flood was classified as a large-scale extreme event. In a Holocene perspective it is suggested that storm berm (Beach Ridge) heights above contemporaneous sea level can be used as a proxy of past flood events along micro-tidal shores.
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changes in holocene relative sea level and coastal morphology a study of a raised Beach Ridge system on samso southwest scandinavia
The Holocene, 2015Co-Authors: Mikkel U Hede, Lasse Sander, Morten Pejrup, Lars B Clemmensen, Aart Kroon, Lars NielsenAbstract:Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised Beach Ridge system on the island of Samso, Denmark. The internal architecture of the Beach Ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the Beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that Beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the Beach steps should be corrected for Beach step height in order to be used as a marker of sea-level. Identification of Beach steps in combination with observed changes in dips of the interpreted Beachface reflections can give information about changes in the morphodynamic conditions of Beach Ridge progradation through time. The vertical levels of identified downlap points are combined with an age m...
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morphology and sedimentary architecture of a Beach Ridge system anholt the kattegat sea a record of punctuated coastal progradation and sea level change over the past 1000 years
Boreas, 2012Co-Authors: Lars B Clemmensen, Mette Bendixen, Lars Nielsen, A S MurrayAbstract:Flakket on the island of Anholt in Denmark is a cuspate foreland facing the microtidal Kattegat sea. It is composed of a number of Beach Ridges typically covered by dune sand and separated by swales and wetlands. OSL dating indicates that the evolution of Flakket began c. AD 1000. Foreland growth was punctuated by a major episode of coastal reorganization leading to coastal retreat c. AD 1800. Coastal retreat led to the formation of an erosion surface that separates older and higher-lying Beach-Ridge and swale deposits from younger and lower-lying deposits. The palaeo-sea level is deduced from the architecture of the deposits, and interpretation of ground-penetrating radar data and geomophological observations indicates that relative sea level was about 1.90±0.25 m above present sea level c. AD 1000, but about 0.00±0.25 m relative to present sea level c. AD 1830 and c. AD 1870. Anholt is situated at the margin of the uplifted Fennoscandian area; assuming uplift to be about 1.2 mm a−1 it follows that absolute sea level was about +0.70±0.25 m at AD 1000, but around −0.22±0.25 m at AD 1830 and around −0.17±0.25 m at AD 1870. Within the uncertainties of the age control, the sea-level indicators mapped by ground-penetrating radar reflections and the variability of estimates of uplift found in the literature, the result obtained for AD 1000 is consistent with findings from the Stockholm area in Sweden and with a recently published global sea-level curve.
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quantitative constraints on the sea level fall that terminated the littorina sea stage southern scandinavia
Quaternary Science Reviews, 2012Co-Authors: Lars B Clemmensen, A S Murray, Lars NielsenAbstract:Abstract The island of Anholt in the Kattegat sea (southern Scandinavia) is made up largely of an extensive Beach-Ridge plain. As a result of post-glacial uplift, the earliest Beach-Ridge and swale deposits are now raised 8–9 m above present mean sea level. It appears that growth of the plain has been almost uninterrupted over the past 7500 years; here we constrain the evolution of this plain between 6300 and 1300 years ago using optically stimulated luminescence dates. The topography and internal architecture of the fossil shoreline deposits were measured on high-resolution maps and in ground-penetrating radar (GPR) reflection data with a vertical resolution of ∼0.25 m. Shoreline topography shows significant changes with time, and it appears that one of the most striking changes took place between 4300 and 3600 years ago; in the shoreline deposits corresponding to this time interval the surface drops by around 3.5 m suggesting a marked fall in relative sea-level. Assuming a constant uplift rate of 1.2 mm/yr, the corresponding drop in absolute sea-level is estimated to be around 2.6 m. This marked sea-level fall in 700 years took place at the transition from the Middle Holocene Thermal Maximum to the Late Holocene Thermal Decline or at the end of the Littorina Sea stage in the Baltic Sea region.
Lars Nielsen - One of the best experts on this subject based on the ideXlab platform.
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sea level proxies in holocene raised Beach Ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Mette Bendixen, Ronny Weβling, Lars B Clemmensen, Aart Kroon, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach Ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach Ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach Ridge systems represent long time intervals and only relatively small spatial extents.
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changes in holocene relative sea level and coastal morphology a study of a raised Beach Ridge system on samso southwest scandinavia
The Holocene, 2015Co-Authors: Mikkel U Hede, Lasse Sander, Morten Pejrup, Lars B Clemmensen, Aart Kroon, Lars NielsenAbstract:Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised Beach Ridge system on the island of Samso, Denmark. The internal architecture of the Beach Ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the Beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that Beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the Beach steps should be corrected for Beach step height in order to be used as a marker of sea-level. Identification of Beach steps in combination with observed changes in dips of the interpreted Beachface reflections can give information about changes in the morphodynamic conditions of Beach Ridge progradation through time. The vertical levels of identified downlap points are combined with an age m...
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morphology and sedimentary architecture of a Beach Ridge system anholt the kattegat sea a record of punctuated coastal progradation and sea level change over the past 1000 years
Boreas, 2012Co-Authors: Lars B Clemmensen, Mette Bendixen, Lars Nielsen, A S MurrayAbstract:Flakket on the island of Anholt in Denmark is a cuspate foreland facing the microtidal Kattegat sea. It is composed of a number of Beach Ridges typically covered by dune sand and separated by swales and wetlands. OSL dating indicates that the evolution of Flakket began c. AD 1000. Foreland growth was punctuated by a major episode of coastal reorganization leading to coastal retreat c. AD 1800. Coastal retreat led to the formation of an erosion surface that separates older and higher-lying Beach-Ridge and swale deposits from younger and lower-lying deposits. The palaeo-sea level is deduced from the architecture of the deposits, and interpretation of ground-penetrating radar data and geomophological observations indicates that relative sea level was about 1.90±0.25 m above present sea level c. AD 1000, but about 0.00±0.25 m relative to present sea level c. AD 1830 and c. AD 1870. Anholt is situated at the margin of the uplifted Fennoscandian area; assuming uplift to be about 1.2 mm a−1 it follows that absolute sea level was about +0.70±0.25 m at AD 1000, but around −0.22±0.25 m at AD 1830 and around −0.17±0.25 m at AD 1870. Within the uncertainties of the age control, the sea-level indicators mapped by ground-penetrating radar reflections and the variability of estimates of uplift found in the literature, the result obtained for AD 1000 is consistent with findings from the Stockholm area in Sweden and with a recently published global sea-level curve.
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quantitative constraints on the sea level fall that terminated the littorina sea stage southern scandinavia
Quaternary Science Reviews, 2012Co-Authors: Lars B Clemmensen, A S Murray, Lars NielsenAbstract:Abstract The island of Anholt in the Kattegat sea (southern Scandinavia) is made up largely of an extensive Beach-Ridge plain. As a result of post-glacial uplift, the earliest Beach-Ridge and swale deposits are now raised 8–9 m above present mean sea level. It appears that growth of the plain has been almost uninterrupted over the past 7500 years; here we constrain the evolution of this plain between 6300 and 1300 years ago using optically stimulated luminescence dates. The topography and internal architecture of the fossil shoreline deposits were measured on high-resolution maps and in ground-penetrating radar (GPR) reflection data with a vertical resolution of ∼0.25 m. Shoreline topography shows significant changes with time, and it appears that one of the most striking changes took place between 4300 and 3600 years ago; in the shoreline deposits corresponding to this time interval the surface drops by around 3.5 m suggesting a marked fall in relative sea-level. Assuming a constant uplift rate of 1.2 mm/yr, the corresponding drop in absolute sea-level is estimated to be around 2.6 m. This marked sea-level fall in 700 years took place at the transition from the Middle Holocene Thermal Maximum to the Late Holocene Thermal Decline or at the end of the Littorina Sea stage in the Baltic Sea region.
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internal architecture of a raised Beach Ridge system anholt denmark resolved by ground penetrating radar investigations
Sedimentary Geology, 2010Co-Authors: Lars B Clemmensen, Lars NielsenAbstract:Abstract The internal architecture of raised Beach Ridge and associated swale deposits on Anholt records an ancient sea level. The Holocene Beach Ridges form part of a progradational Beach Ridge plain, which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years. The Ridges are covered by pebbles and cobbles and commonly show evidence of deflation. Material presumably removed from the Beach Ridges and adjacent swales form the present dune forms on Anholt. Ground-penetrating radar (GPR) reflection lines have been collected with 250 MHz shielded antennae across the fossil Ridge and swale structures. The signals penetrate the subsurface to a maximum depth of ∼ 10 m below the fossil features. The GPR data resolve the internal architecture of the Beach Ridges and swales with a vertical resolution of about 0.1 m. GPR mapping indicates that the Holocene Beach Ridges are composed of seaward-dipping Beachface deposits as well as minor amounts of inland dipping deposits of wash-over origin. The Beachface deposits downlap on underlying shoreface deposits, and we use these surfaces as markers of a relative palaeo-sea level. The new data indicate that the highest relative sea level at about 8.5 m was reached 6500 years ago; 700 years later the relative sea level had dropped 0.7 m indicating a change in the relative sea level around 1 mm/year. This fall in the relative sea level most likely records the influence of an isostatic rebound causing younger Beach Ridge deposits to indicate lower sea levels.
A S Murray - One of the best experts on this subject based on the ideXlab platform.
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measurement of natural radioactivity calibration and performance of a high resolution gamma spectrometry facility
Radiation Measurements, 2018Co-Authors: A S Murray, Janpieter Buylaert, L M Helsted, Martin Autzen, Mayank JainAbstract:Abstract Murray et al. (2015) described an international inter-comparison of dose rate measurements undertaken using a homogenised Beach Ridge sand from Jutland, Denmark. The measured concentrations for 226 Ra, 232 Th and 40 K from different laboratories varied considerably, with relative standard deviations of 26% (n = 8), 59% (n = 23) and 15% (n = 23), respectively. In contrast, the relative standard deviations observed internally within our laboratory were 9%, 11% and 7%, respectively (n = 20), and in addition our mean values were consistent with the global 40 K mean, but significantly different from the 232 Th mean. These problems in both accuracy and precision have led us to examine both the long term performance of our analytical facility, and its calibration. Our approach to the preparation of new absolute 238 U, 232 Th and 40 K standards is outlined and tested against international standards. We also report analyses of the Volkegem (De Corte et al., 2007) and Nussi (Preusser and Kasper, 2001) loess samples, for further comparison with other laboratories.
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a luminescence dating intercomparison based on a danish Beach Ridge sand
Radiation Measurements, 2015Co-Authors: A S Murray, Janpieter Buylaert, Christine ThielAbstract:Abstract There is a need for large scale intercomparisons to determine the degree of coherence of luminescence dating measurements made by different laboratories. Here we describe results from a laboratory intercomparison sample based on a quartz-rich aeolian and/or coastal marine sand Ridge from the Skagen peninsula, northern Jutland (Denmark). About 200 kg of sand was sampled at night from a single Beach Ridge. The sand was homogenised using a cement mixer and packed in ∼700 moisture and light-tight bags for distribution. The quartz luminescence characteristics are satisfactory (e.g. fast-component dominated and good dose recovery) and our own equivalent dose determinations and measurements of radionuclide concentrations for twenty of these bags demonstrate the degree of homogenisation. One natural sample and one sample of pre-processed quartz was made available on request; analysis of all the responses gives a mean dose (pre-processed quartz) of 4.58 Gy, σ = 0.40 (n = 26), to be compared to the mean dose (self-extracted quartz) of 4.52 Gy, σ = 0.55 (n = 21). The mean age is 3.99 ± 0.14 ka, σ = 0.71 (n = 22), i.e. a relative standard deviation of 18%. We present an analysis of all the important quantitative and qualitative responses we received between 2007 and 2012 and discuss the implications for our dating community and for users of luminescence ages.
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morphology and sedimentary architecture of a Beach Ridge system anholt the kattegat sea a record of punctuated coastal progradation and sea level change over the past 1000 years
Boreas, 2012Co-Authors: Lars B Clemmensen, Mette Bendixen, Lars Nielsen, A S MurrayAbstract:Flakket on the island of Anholt in Denmark is a cuspate foreland facing the microtidal Kattegat sea. It is composed of a number of Beach Ridges typically covered by dune sand and separated by swales and wetlands. OSL dating indicates that the evolution of Flakket began c. AD 1000. Foreland growth was punctuated by a major episode of coastal reorganization leading to coastal retreat c. AD 1800. Coastal retreat led to the formation of an erosion surface that separates older and higher-lying Beach-Ridge and swale deposits from younger and lower-lying deposits. The palaeo-sea level is deduced from the architecture of the deposits, and interpretation of ground-penetrating radar data and geomophological observations indicates that relative sea level was about 1.90±0.25 m above present sea level c. AD 1000, but about 0.00±0.25 m relative to present sea level c. AD 1830 and c. AD 1870. Anholt is situated at the margin of the uplifted Fennoscandian area; assuming uplift to be about 1.2 mm a−1 it follows that absolute sea level was about +0.70±0.25 m at AD 1000, but around −0.22±0.25 m at AD 1830 and around −0.17±0.25 m at AD 1870. Within the uncertainties of the age control, the sea-level indicators mapped by ground-penetrating radar reflections and the variability of estimates of uplift found in the literature, the result obtained for AD 1000 is consistent with findings from the Stockholm area in Sweden and with a recently published global sea-level curve.
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quantitative constraints on the sea level fall that terminated the littorina sea stage southern scandinavia
Quaternary Science Reviews, 2012Co-Authors: Lars B Clemmensen, A S Murray, Lars NielsenAbstract:Abstract The island of Anholt in the Kattegat sea (southern Scandinavia) is made up largely of an extensive Beach-Ridge plain. As a result of post-glacial uplift, the earliest Beach-Ridge and swale deposits are now raised 8–9 m above present mean sea level. It appears that growth of the plain has been almost uninterrupted over the past 7500 years; here we constrain the evolution of this plain between 6300 and 1300 years ago using optically stimulated luminescence dates. The topography and internal architecture of the fossil shoreline deposits were measured on high-resolution maps and in ground-penetrating radar (GPR) reflection data with a vertical resolution of ∼0.25 m. Shoreline topography shows significant changes with time, and it appears that one of the most striking changes took place between 4300 and 3600 years ago; in the shoreline deposits corresponding to this time interval the surface drops by around 3.5 m suggesting a marked fall in relative sea-level. Assuming a constant uplift rate of 1.2 mm/yr, the corresponding drop in absolute sea-level is estimated to be around 2.6 m. This marked sea-level fall in 700 years took place at the transition from the Middle Holocene Thermal Maximum to the Late Holocene Thermal Decline or at the end of the Littorina Sea stage in the Baltic Sea region.
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new evidence of the littorina transgressions in the kattegat optically stimulated luminescence dating of a Beach Ridge system on anholt denmark
Boreas, 2008Co-Authors: Mette Bjornsen, Lars B Clemmensen, A S Murray, Karsten PedersenAbstract:Recent geomorphological and sedimentological investigation of the raised Beach Ridge plain on Anholt in the Kattegat Sea, Denmark, has demonstrated how these deposits, when combined with Optically Stimulated Luminescence (OSL) dating, can provide information about past changes in relative sea level. The southwest–northeast trending plain is divided into three topographic levels, one of which has been surveyed using Ground-Penetrating Radar (GPR). Samples retrieved from the survey line indicate that the initial part of the Beach Ridge plain formed about 7700 years ago in response to a mid-Holocene Littorina transgression. The raised marine deposits document a subsequent rise in relative sea level of about 9 m, and OSL dates indicate that this transgression took place about 6650 years ago. The flooding of the Kattegat Sea 7700 years ago might possibly be related to a rapid global sea-level rise peaking around 7500 years ago.
Aart Kroon - One of the best experts on this subject based on the ideXlab platform.
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sea level proxies in holocene raised Beach Ridge deposits greenland revealed by ground penetrating radar
Scientific Reports, 2017Co-Authors: Lars Nielsen, Mikkel U Hede, Mette Bendixen, Ronny Weβling, Lars B Clemmensen, Aart Kroon, Bo ElberlingAbstract:Identification of sea-level proxies is important for reconstruction of past sea-level variation. Methods for reconstructing Holocene relative sea-level curves are crucial for quantification of the impact of Greenland ice thickness variation on global sea level and vertical land movement. Arctic Beach Ridges constitute important potential archives of sea-level variation. However, their surface morphology may have undergone modification since deposition due to freezing/thawing processes and erosion, and their morphology may therefore not be trustworthy for sea-level reconstruction. Therefore, geophysical imaging is used to examine the internal structures of the Beach Ridges and to define a sea-level proxy unaffected by surface processes. The GPR reflections from study sites in West and South Greenland show deposition of Beachface deposits and upper shoreface deposits; the contact between steeply dipping Beachface reflections and less-dipping shoreface reflections is used as sea-level proxy. Numerous points are identified along GPR transects facilitating reconstruction of relative sea-level variation of hitherto unprecedented resolution. Erosional events and deformation caused by freezing/thawing processes are clearly delineated. The approach constitutes a solid base for reconstruction of relative sea-level curves affected by a well-defined vertical land movement history since the studied Beach Ridge systems represent long time intervals and only relatively small spatial extents.
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storm flood impacts along the shores of micro tidal inland seas a morphological and sedimentological study of the vesterlyng Beach the belt sea denmark
Geomorphology, 2016Co-Authors: Lars B Clemmensen, Aslaug C Glad, Aart KroonAbstract:Abstract The morphological and sedimentological impacts of an extreme storm event (‘Bodil’ in December 2013) were investigated at a mixed sand and gravel Beach (Vesterlyng) in a micro-tidal environment along the Belt Sea, Denmark. The storm response was characteristic for mixed sand and gravel Beaches: gravelly storm berms with sandy to gravelly washover fans were formed at the upper Beach where swash processes dominated during extreme water levels in combination with overtopping and overwash. In addition, storm scarps and gravel flats were formed. The elevation of the storm berm crest was identical to a summation of the still-water level (1.60 m) in the Belt Sea during the storm flood and the wave run-up (0.75 m) at the shore. The crest of 2.35 m is therefore a precise measure of the storm flood level. This storm flood was classified as a large-scale extreme event. In a Holocene perspective it is suggested that storm berm (Beach Ridge) heights above contemporaneous sea level can be used as a proxy of past flood events along micro-tidal shores.
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changes in holocene relative sea level and coastal morphology a study of a raised Beach Ridge system on samso southwest scandinavia
The Holocene, 2015Co-Authors: Mikkel U Hede, Lasse Sander, Morten Pejrup, Lars B Clemmensen, Aart Kroon, Lars NielsenAbstract:Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised Beach Ridge system on the island of Samso, Denmark. The internal architecture of the Beach Ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the Beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that Beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the Beach steps should be corrected for Beach step height in order to be used as a marker of sea-level. Identification of Beach steps in combination with observed changes in dips of the interpreted Beachface reflections can give information about changes in the morphodynamic conditions of Beach Ridge progradation through time. The vertical levels of identified downlap points are combined with an age m...
Yoshiki Saito - One of the best experts on this subject based on the ideXlab platform.
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palaeogeography and evolution of the godavari delta east coast of india during the holocene an example of wave dominated and fan delta settings
Palaeogeography Palaeoclimatology Palaeoecology, 2015Co-Authors: Kakani Nageswara Rao, Yoshiki Saito, Ch K V Nagakumar, G Demudu, A S Rajawat, Sumiko KuboAbstract:Abstract We investigated the Holocene evolution of the Godavari delta along the east coast of India, by analyses of landforms and 11 borehole cores collected from the delta plain during 2010–2013 with 113 14C dates. The Godavari delta covering an area of 5820 km2 is one of the world's largest wave-dominated deltas fringed by a ~ 30 km wide Beach-Ridge plain. Our analysis of sediment facies and their ages indicated that the Holocene marine sequence thickens seaward from ~ 10 m to more than 50 m and that the local relative sea level rapidly rose from 43.5 m to 7.5 m below the present sea level during 10.9–8.0 cal ky BP followed by a slow rise up to its current level around 5 cal ky BP. Spatio-temporal variations in sediment accumulation rates and palaeo-shorelines for the last 6 ky revealed successive changes of the main depocentre (delta lobe). We recognised six stages of delta evolution with distinct cyclic shifts of delta lobes controlled by avulsions. A linear Beach Ridge located 12–14 km inland from the present shoreline, which separates the first three lobes from the last three, represents the effect of coastal erosion of past cuspate delta lobes, as does the current linear shoreline of the central part of the delta. Our study documents continuous net progradation during the Holocene on millennial to centennial time scales. However, a considerable decrease of sediment discharge due to dam construction and water diversion since the 1970s has exacerbated coastal erosion, resulting in shrinking of the Godavari delta plain and tipping it into a persistent destruction phase.
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mid to late holocene sea level reconstruction of southeast vietnam using Beachrock and Beach Ridge deposits
Global and Planetary Change, 2013Co-Authors: Karl Stattegger, Rik Tjallingii, Yoshiki Saito, Maximiliano Michelli, Nguyen Trung Thanh, Andreas WetzelAbstract:Beachrocks, Beach Ridge, washover and backshore deposits along the tectonically stable south-eastern Vietnamese coast document Holocene sea level changes. In combination with data from the final marine flooding phase of the incised Mekong River valley, the sea-level history of South Vietnam could be reconstructed for the last 8000 years. Connecting saltmarsh, mangrove and Beachrock deposits the record covers the last phase of deglacial sea-level rise from − 5 to + 1.4 m between 8.1 to 6.4 ka. The rates of sea-level rise decreased sharply after the rapid early Holocene rise and stabilized at a rate of 4.5 mm/year between 8.0 and 6.9 ka. Southeast Vietnam Beachrocks reveal that the mid-Holocene sea-level highstand slightly above + 1.4 m was reached between 6.7 and 5.0 ka, with a peak value close to + 1.5 m around 6.0 ka. This highstand is further limited by a backshore and BeachRidge deposit that marks the maximum springtide sea-level just below the base of the overlying Beach Ridge. After 5.0 ka sea level dropped below + 1.4 m and fell almost linearly at a rate of 0.24 mm/year until 0.63 ka and + 0.2 m as evidenced by the youngest Beachrocks. The Holocene sea-level fluctuations observed in Southeast Vietnam resulted from eustatic and isostatic processes. The sea-level rise up to the mid-Holocene highstand was provoked by the last melting phase of glacial polar ice-sheets. The sea-level drop after the mid-Holocene highstand was induced by the isostatic processes of continental levering with an uplift of continents in low latitudes and depression of adjacent flooded continental shelf areas and Equatorial Ocean Siphoning transferring oceanic waters from low latitudes to the increasing volume of oceanic basins in higher latitudes. The regional expression in terms of magnitude and timing of relative sea-level change might contribute to validation of geophysical model simulations.